New, improved, advanced resists are required to manufacture new electronic devices with smaller feature sizes. Typically, improvements are required in photoresist resolution, photospeed, depth of focus, and other properties. Resolution improvements can also be obtained via exposure systems utilizing higher numerical apertures. Unfortunately, as the resolution is improved via higher numerical apertures, the depth of focus at best resolution usually decreases due to optical effects. Thus, improvements in depth of focus of resist are also desirable.
The most common type of resists are called “single layer” resists in which the resist has both the function of imaging and plasma etch resistance. A second type of resist is termed a “bilayer resist” in which the top layer is assigned the function of imaging and the underlayer assigned the function of plasma etch resistance. An oxygen etch step transfers the imaged pattern into the underlayer. Bilayer resists typically contain silicon and provide certain advantages in resolution from using thinner imaging films and in many cases the bilayer resist/undercoat combination provide better substrate plasma etch resistance. Examples of bilayer resists can be found for example in U.S. Pat. No. 6,359,078, U.S. Pat. No. 5,985,524 and U.S. Pat. No. 6,028,154 and other patents, each of which is incorporated herein in their entirety.
Photoresists based on silsesquioxane polymers as the polymeric backbone have been reported in U.S. Pat. No. 6,420,084 and other patents. Polyhedral oligomeric silsesquioxanes are characterized by low molecular weight and closed or partially open cage structures having specific numbers of silicon atoms at the vertices of the cage. Polyhedral oligomeric silsesquioxanes when incorporated into polymers are typically pendant from the polymer chain rather than forming the polymer backbone and have a lower concentration relative to typical silsesquioxane polymers. There are few reports of photosensitive compositions containing polyhedral oligomeric silsesquioxanes (POSS®) in which the polyhedral oligomeric silsesquioxane is pendant from the polymer backbone (see U.S. patent application Ser. No. 09/992,560, published as US 2002/0182541 A1).